Method for transmitting channel state information in wireless access system

ABSTRACT

Channel State Information (CSI) is reported by a user equipment (UE) in a wireless access system which supports carrier aggregation. A first type CSI for a first component carrier (CC) of two or more downlink (DL) CCs is measured. A second type CSI for a second CC of the two or more downlink (DL) CCs is measured. The first type CSI only is reported, when a collision of a report of the first type CSI with a report of the second CSI type is occurred in a same subframe. In addition, the first type CSI includes (1) a Rank indicator (RI) and a first Precoding Matrix Indicator (PMI), (2) only the RI, or (3) only the first PMI, and the second type CSI includes (1) a Wideband Channel Quality Indicator (WB-CQI) and a second PMI, (2) the WB-CQI and the first PMI, or (3) only the WB-CQI.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. patent applicationSer. No. 13/734,798 filed on Jan. 4, 2013, which is a continuation ofU.S. patent application Ser. No. 13/638,514 filed on Sep. 28, 2012 nowU.S. Pat. No. 8,995,373, issued on Mar. 31, 2015), which is the NationalPhase of PCT/KR2011/002289 filed on Apr. 1, 2011, which claims priorityunder 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/320,307filed on Apr. 1, 2010 and to U.S. Provisional Application No. 61/389,698filed on Oct. 4, 2010, all of which are hereby expressly incorporated byreference into the present application,

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless access system, and moreparticularly, to various methods for transmitting channel stateinformation on one or more serving cells in a carrier aggregationenvironment and apparatuses for supporting the same.

2. Discussion of the Related Art

In a general wireless access system, only one carrier is generallyconsidered even though uplink (UL) and downlink (DL) bandwidths aredifferently configured. For example, a wireless communication system inwhich the number of carriers constituting each of UL and DL is one and aUL bandwidth and a DL bandwidth are generally symmetrical may beprovided based on a single carrier.

In the International Telecommunication Union (ITU), an IMT-Advancedcandidate technique demands support of an extended bandwidth comparedwith a conventional wireless communication system. However, it is noteasy to allocate frequency of a wide bandwidth except in some areas ofthe world. Accordingly, a carrier aggregation (also called bandwidthaggregation or spectrum aggregation) technique for producing an effectas if a broadband is logically used by physically aggregating aplurality of bands in the frequency domain has been developed as atechnique for efficiently using a fragmented narrowband.

Carrier aggregation has been introduced to support increased throughput,prevent cost increase caused by introduction of a broadband RF element,and ensure compatibility with existing systems. Carrier aggregationrefers to a technique for exchanging data between a User Equipment (UE)and a Base Station (BS) through plural aggregates of carriers in theunit of a bandwidth defined in an existing wireless access system (anLTE system in case of an LTE-A system, or an IEEE 802.16e system in caseof an IEEE 802.16m system).

Here, a carrier of the unit of a bandwidth defined in an existingwireless communication system may be called a Component Carrier (CC).Carrier aggregation may include a technique supporting a systembandwidth of up to a maximum of 100 MHz by aggregating a maximum of 5CCs even if one CC supports, for example, a bandwidth of 5 MHz, 10 MHzor 20 MHz.

When using the carrier aggregation technique, data can be simultaneouslytransmitted and received through multiple UL/DL CCs. Hence, a UE iscapable of monitoring and calculating all CCs.

SUMMARY OF THE INVENTION

To reduce distortion of a power amplifier during UL transmission of aUE, a single carrier property needs to be maintained with respect to aUL transmission signal. To this end, it is necessary to define a UEbehavior for maintaining a single carrier property of a UL transmissionsignal when a plurality of Physical Uplink Control Channels (PUCCHs)should be transmitted through the same subframe.

In one subframe, a UE should transmit control information for oneserving cell. If Channel State Information (CSI) for one or more cellsis transmitted through the same subframe, a UE behavior for CSIreporting needs to be defined.

Accordingly, it is an object of the present invention to define a UEbehavior in UL for CSI transmission for multiple serving cells in amulticarrier aggregation environment.

It is another object of the present invention to provide a methodcapable of transmitting one piece of control information (i.e. CSI)through one PUCCH, when CSI transmission for a plurality of servingcells is simultaneously demanded through a plurality of PUCCHs in aspecific subframe.

It is still another object of the present invention to provide a methodfor dropping CSI according to priority so that specific CSI alone can betransmitted among plural pieces of CSI. For example, a method isprovided through which a UE drops specific CSI according to cell type,CSI transmission period, and/or CSI type.

It will be appreciated by persons skilled in the art that that thetechnical objects that can be achieved through the present invention arenot limited to what has been particularly described hereinabove andother technical objects of the present invention will be more clearlyunderstood from the following detailed description.

To achieve the above technical object, the present invention disclosesvarious methods for transmitting CSI for one or more serving cells in acarrier aggregation environment and apparatuses for supporting the same.

According to one aspect of the present invention, a method for reportingChannel State Information (CSI) in a wireless access system whichsupports carrier aggregation includes receiving, at a User Equipment(UE), information related to a CSI reporting mode for one or moreserving cells from a Base Station (BS) and reporting, at the UE, one ormore CSI for the one or more serving cells to the BS in consideration ofthe CSI reporting mode, wherein, if first type CSI for a first servingcell and second type CSI for a second serving cell are transmitted inthe same subframe, the UE reports only CSI for one serving cell to theBS according to priority of a CSI reporting type related to the CSIreporting mode.

According to another aspect of the present invention, a method forreceiving Channel State Information (CSI) in a wireless access systemwhich supports carrier aggregation includes transmitting, at a BaseStation (BS), information related to a CSI reporting mode for one ormore serving cells to a User Equipment (UE), and receiving one or morereports on one or more CSI for the one or more serving cells consideringthe CSI reporting mode from the UE, wherein, if first type CSI for afirst serving cell and second type CSI for a second serving cell aretransmitted in the same subframe, the BS receives only CSI for oneserving cell according to priority of a CSI reporting type related tothe CSI reporting mode.

According to a further aspect of the present invention, a User Equipment(UE) for reporting Channel State Information (CSI) in a wireless accesssystem which supports carrier aggregation includes a transmission modulefor transmitting a channel signal, a reception module for receiving achannel signal, and a processor for supporting CSI reporting, whereinthe UE receives information related to a CSI reporting mode for one ormore serving cells through the reception module from a Base Station (BS)and reports one or more CSI for the one or more serving cells to the BSin consideration of the CSI reporting mode, and if first type CSI for afirst serving cell and second type CSI for a second serving cell aretransmitted in the same subframe, the UE reports only CSI for oneserving cell to the BS according to priority of a CSI reporting typerelated to the CSI reporting mode.

In the above aspects of the present invention, if priority of the firsttype CSI is higher than priority of the second type CSI, the UE maytransmit only the first type CSI to the BS and drop the second type CSI.

The first type CSI may indicate that the UE reports a Rank Indicator(RI) and a first Precoding Matrix indicator (PMI) or only the RI to theBS and the second type CSI may indicate that the UE reports a WidebandChannel Quality Indicator (WB-CQI) and a second PMI, the WB-CQI and thefirst PMI, or only the WB-CQI to the BS.

The first type CSI may indicate that the UE reports a WB-CQI and asecond PMI, the WB-CQI and a first PMI, or only the WB-CQI to the BS andthe second type CSI may indicate that the UE reports a Subband CQI(SB-CQI) and the second PMI or only the SB-CQI to the BS.

The first type CSI may indicate that the UE reports an RI and a firstPMI or only the RI to the BS and the second type CSI may indicate thatthe UE reports an SB-CQI and a second PMI or only the SB-CQI to the BS.

In the above aspects of the present invention, the first type CSI andthe second type CSI may be configured to support the CSI reporting mode.

In the above aspects of the present invention, reporting the CSI isperiodically performed according to each content of the CSI.

In the above aspects of the present invention, the first type CSI may bea CSI reporting type 3 or CSI reporting type 5 and the second type CSImay be a CSI reporting type 2, a CSI reporting type 2c, a CSI reportingtype 4, a CSI reporting type 1, or a CSI reporting type 1a.

Alternatively, the first type CSI may be a CSI reporting type 2b, a CSIreporting type 2c, or a CSI reporting type 4 and the second type CSI maybe a CSI reporting type 1 or a CSI reporting type 1a.

In the above aspects of the present invention, the first type CSI may betransmitted to the BS through a Physical Uplink Control Channel (PUCCH)and a Physical Uplink Shared Channel (PUSCH). If the first type CSI istransmitted through the PUSCH, the first type CSI may be piggybacked ormultiplexed on uplink data and then transmitted. For example, if the UEis in a simultaneous transmission mode of PUSCH and PUCCH signals, thefirst type CSI is transmitted through the PUCCH, and if the UE is in anindividual transmission mode of a PUSCH and PUCCH signal, the first typeCSI is transmitted through the PUSCH by being piggybacked on uplinkdata.

The above aspects of the present invention are merely some parts of theexemplary embodiments of the present invention and other embodimentsinto which the technical features of the present invention areincorporated can be derived and understood by those skilled in the artfrom the detailed description of the present invention which follows.

The embodiments of the present invention have the following effects.

First, a single carrier property for a UL transmission signal during ULtransmission of a UE can be maintained using the embodiments of thepresent invention.

Second, when CSI for one or more serving cells is transmitted throughthe same subframe, collision between CSI can be prevented by reportingCSI according to defined UE behavior for CSI reporting. Namely, CSI maybe dropped according to priority so as to transmit specific CSI aloneamong plural pieces of CSI, thereby preventing collision between CSI.

Third, when CSI transmission for a plurality of serving cells issimultaneously demanded through a plurality of PUCCHs in the samesubframe, one piece of control information (i.e. CSI) can be transmittedthrough one PUCCH.

It will be appreciated by persons skilled in the art that that theeffects that can be achieved through the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a radio frame structure which can beused in embodiments of the present invention;

FIG. 2 is a diagram illustrating a resource grid for one DL slot whichcan be used in embodiments of the present invention;

FIG. 3 is a diagram illustrating a DL subframe structure which can beused in embodiments of the present invention;

FIG. 4 is a diagram illustrating a UL subframe structure which can beused in embodiments of the present invention;

FIG. 5 is a diagram illustrating one of UL CQI transmission methods;

FIG. 6 is a diagram illustrating frequency band selective CQI generationmethods;

FIG. 7, including (a) and (b), is a diagram illustrating an example of aCC used in an LTE system and multiple carriers (carrier aggregation)used in an LTE-A system;

FIG. 8 is a diagram illustrating an exemplary cross-CC scheduling methodwhich can be used in the present invention;

FIG. 9 is a diagram illustrating a CSI report method according topriority of CSI in accordance with an embodiment of the presentinvention;

FIG. 10 is a diagram illustrating a CSI drop method according to celltype in accordance with an embodiment of the present invention;

FIG. 11 is a diagram illustrating a CSI drop method according to a CSIreporting period in accordance with an embodiment of the presentinvention;

FIG. 12 is a diagram illustrating a CSI drop method according to a CSItype in accordance with an embodiment of the present invention;

FIG. 13 is a diagram illustrating another CSI drop method according toCSI type in accordance with an embodiment of the present invention;

FIG. 14 is a diagram illustrating the linkage between 100 UL RBs and 100DL PHICH resources which can be referred to in embodiments of thepresent invention;

FIGS. 15 to 19 are diagrams illustrating exemplary PHICH resourceallocation methods in accordance with embodiments of the presentinvention; and

FIG. 20 is a diagram illustrating an apparatus for supporting a CSItransmission method disclosed in the present invention in accordancewith an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention disclose various methods fortransmitting CSI for one or more serving cells in a carrier aggregationenvironment and apparatuses for supporting the same and also disclosePHICH allocation methods.

The following embodiments are realized by combinations of elements andfeatures of the present invention in a predetermined form. It may beconsidered that the elements or features are optional unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment.

In the description of the drawings, procedures or steps, which mayobscure the substance of the present invention, are not explained. Inaddition, procedures or steps, which can be understood by those skilledin the art, are not explained.

In the exemplary embodiments of the present invention, a description isgiven of data transmission and reception between a Base Station (BS) anda Mobile Station (MS). Here, the term ‘BS’ refers to a terminal node ofa network communicating directly with the MS. In some cases, a specificoperation described as being performed by the BS may be performed by anupper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with an MS may be performed by the BS, or network nodesother than the BS. The term ‘BS’ may be replaced with terms such asfixed station, Node B, eNode B (eNB), Advanced Base Station (ABS),access point, etc.

The term ‘MS’ may be replaced with terms such as User Equipment (UE),Subscriber Station (SS), Mobile Subscriber Station (MSS), mobileterminal, Advanced Mobile Station (AMS), terminal, etc.

A transmitting end refers to a fixed and/or mobile node which transmitsa data service or a voice service and a receiving end refers to a fixedand/or mobile node which receives a data service or a voice service.Therefore, in UL, an MS may be a transmitting end and a BS may be areceiving end. Similarly, in DL, the MS may be a receiving end and theBS may be a transmitting end.

The embodiments of the present invention can be supported by standarddocuments disclosed in at least one of wireless access systems includingan IEEE 802.xx system, a 3rd Generation Partnership Project (3GPP)system, a 3GPP LTE system, and a 3GPP2 system. Especially, theembodiments of the present invention can be supported by 3GPP TS 36.211,3GPP TS 36.212, 3GPP TS 36.213, and 3GPP TS 36.321 documents. That is,obvious steps or portions that are not described in the embodiments ofthe present invention can be described with reference to the abovedocuments. In additional, for description of all terms used herein,reference can be made to the above standard documents.

Reference will now be made in detail to the exemplary embodiments of thepresent invention in conjunction with the accompanying drawings. Thedetailed description, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present invention, rather than to show the only embodiments that canbe implemented according to the invention.

In addition, the specific terms used in the embodiments of the presentinvention are provided to aid in understanding of the present inventionand those terms may be changed without departing from the spirit of thepresent invention.

The following technology can be used for a variety of radio accesstechniques, for example, Code Division Multiple Access (CDMA), FrequencyDivision Multiple Access (FDMA), Time Division Multiple Access (TDMA),Orthogonal Frequency Division Multiple Access (OFDMA), and SingleCarrier Frequency Division Multiple Access (SC-FDMA).

CDMA may be embodied through radio technology such as UniversalTerrestrial Radio Access (UTRA) or CDMA2000. TDMA may be embodiedthrough radio technology such as Global System for Mobile communications(GSM)/General Packet Radio Service (GPRS)/Enhanced Data Rates for GSMEvolution (EDGE). OFDMA may be embodied through radio technology such asIEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMax), IEEE 802-20, and Evolved UTRA(E-UTRA).

UTRA is a part of the Universal Mobile Telecommunications System (UMTS).3GPP Long Term Evolution (LTE) is a part of Evolved UMTS (E-UMTS)employing E-UTRA and uses OFDMA in DL and SC-FDMA in UL. An LTE-Advanced(LTE-A) system is an evolved version of a 3GPP LTE system. To clarifydescription of technical features of the present invention, although3GPP LTE/LTE-A is mainly described, the technical sprit of the presentinvention is not limited thereto.

1. Basic Structure of 3GPP LTE/LTE-A System

FIG. 1 is a diagram illustrating a radio frame structure which can beused in embodiments of the present invention.

A radio frame includes 10 subframes and each subframe includes twoslots. A time for transmitting a subframe is defined as a TransmissionTime Interval (TTI). One subframe has a length of 1 ms and one slot hasa length of 0.5 ms.

One slot includes a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols in the time domain and a plurality ofResource Blocks (RBs) in the frequency domain. The OFDM symbol expressesone symbol period in a 3GPP LTE system using an Orthogonal FrequencyDivision Multiplexing Access (OFDMA) scheme on DL. That is, the OFDMsymbol may be called an SC-FDMA symbol or symbol period according to amultiple access scheme. An RB is a resource allocation unit and includesa plurality of consecutive subcarriers in one slot.

The radio frame structure shown in FIG. 1 is purely exemplary andvarious modifications may be made in the number of subframes included inthe radio frame, the number of slots included in the subframe, and thenumber of OFDM symbols included in the slot.

FIG. 2 illustrates a resource grid for one DL slot which can be used inembodiments of the present invention.

A DL slot includes a plurality of OFDM symbols in the time domain. Inthe illustrated example of FIG. 2, one DL slot includes 7 OFDM symbolsand one RB includes 12 subcarriers in the frequency domain.

Each element on a resource grid is referred to as a Resource Element(RE). One RB includes 12×7 REs. The number of RBs included in a DL slot,N^(DL), depends on DL transmission bandwidth.

FIG. 3 is a diagram illustrating a DL subframe structure which can beused in embodiments of the present invention.

A subframe includes two slots in the time domain. A maximum of 3 OFDMsymbols in the front portion of the first slot in a subframe correspondsto a control region to which control channels are allocated and theremaining OFDM symbols correspond to a data region to which a PhysicalDownlink Shared Channel (PDSCH) is allocated.

DL control channels used in a 3GPP LTE system include a Physical ControlFormat Indicator Channel (PCFICH), a Physical Downlink Control Channel(PDCCH), and a Physical Hybrid-ARQ Indicator Channel (PHICH). A PCFICHsignal transmitted on the first OFDM symbol of a subframe carriesinformation about the number of OFDM symbols (i.e. the magnitude of thecontrol region) used for control channel signal transmission in thesubframe. The PHICH carries an Acknowledgment/Negative-Acknowledgment(ACK/NACK) signal for a UL Hybrid Automatic Repeat Request (HARQ). Inother words, the ACK/NACK signal for UL data transmitted by a UE istransmitted over the PHICH.

DL control information transmitted through the PDCCH is referred to asDownlink Control Information (DCI). The DCI includes resource allocationinformation for a UE or a UE group and includes other controlinformation. For example, the DCI may include UL resource allocationinformation, DL resource allocation information, a UL transmit powercontrol command, etc.

The PDCCH may carry a transmission format and resource allocationinformation for a Downlink Shared Channel (DL-SCH), a transmissionformat and resource allocation information for an Uplink Shared Channel(UL-SCH), paging information on a Paging Channel (PCH), systeminformation on the DL-SCH, resource allocation information for ahigher-layer control message such as a random access responsetransmitted on the PDSCH, a transmit power control command set forindividual UEs in a UE group, a transmit power control command,activation information of a Voice over IP (VoIP), and the like.

A plurality of PDCCHs may be transmitted in the control region. A UE maymonitor a plurality of PDCCHs. The PDCCH is transmitted on one or moreconsecutive Control Channel Elements (CCEs). A CCE is a logicalallocation unit used to provide the PDCCH with a coding rate based on aradio channel state. The CCE corresponds to a plurality of ResourceElement Groups (REGs). A format of the PDCCH and the number of availablebits of the PDCCH are determined according to the correlation between acode rate provided in the CCE and the number of CCEs. A BS determinesthe PDCCH format according to DCI to be transmitted to a UE and attachesa Cyclic Redundancy Check (CRC) to control information.

The CRC is masked together with a Radio Network Temporary Identifier(RNTI) according to the used method or owner of the PDCCH. If the PDCCHis dedicated to a specific UE, an identifier of the UE (e.g. cell-RNTI(C-RNTI)) is masked to the CRC. If the PDCCH is dedicated to a pagingmessage, a paging identifier (e.g. paging-RNTI (P-RNTI)) is masked tothe CRC. If the PDCCH is for system information (especially, a systeminformation block), a system information identifier and a systeminformation RNTI (S-RNTI) may be masked to the CRC. A Random Access RNTI(RA-RNTI) may be masked to the CRC in order to indicate a random accessresponse to reception of a random access preamble of a UE.

In a carrier aggregation environment, a PDCCH may be transmitted throughone or more CCs and include resource allocation information for one ormore CCs. For example, although the PDCCH is transmitted through one CC,the PDCCH may include resource allocation information for one or morePDSCHs and PUSCHs.

FIG. 4 is a diagram illustrating a UL subframe structure which can beused in embodiments of the present invention;

Referring to FIG. 4, a UL subframe includes plural (e.g. two) slots.Each slot may include a different number of SC-FDMA symbols according tothe length of a Cyclic Prefix (CP). The UL subframe is divided into adata region and a control region in the frequency domain. The dataregion includes a Physical Uplink Shared Channel (PUSCH) and is used totransmit data signals including voice information. The control regionincludes a PUCCH and is used to transmit Uplink Control Information(DCI). The PUCCH includes an RB pair located at both ends of the dataregion in the frequency domain and is hopped using the slot as aboundary. In an LTE system, a UE does not transmit a PUCCH signal andPUSCH signal at the same time in order to maintain a single carrierproperty.

A PUCCH for one UE is allocated in an RB pair in a subframe and RBsbelonging to the RB pair occupy different subcarriers in each of twoslots. Thus, the RB pair allocated to the PUCCH is ‘frequency-hopped’ ata slot boundary.

The PUCCH may be used to transmit the following control information.

Scheduling Request (SR): SR is used for requesting UL-SCH resources andis transmitted using an On-Off Keying (OOK) scheme.

HARQ ACK/NACK: HARQ ACK/NACK is a response signal to a DL data packet ona PDSCH. HARQ ACK/NACK indicates whether or not a DL data packet hasbeen successfully received. 1-bit. ACK/NACK is transmitted as a responseto a single DL codeword, and 2-bit ACK/NACK is transmitted as a responseto two DL codewords.

Channel Quality Indicator (CQI): CQI is feedback information for a DLchannel. Multiple Input Multiple Output (MIMO)-associated feedbackinformation includes a Rank Indicator (RI) and a Precoding MatrixIndicator (PMI). 20 bits are used per subframe.

The amount of UCI that can be transmitted in a subframe by a UE isdependent upon the number of SC-FDMA symbols available for UCItransmission. The SC-FDMA symbols available for UCI transmissionindicate the remaining SC-FDMA symbols other than SC-FDMA symbols thatare used for reference signal transmission in a subframe. In the case ofa subframe in which a Sounding Reference Signal (SRS) is configured, thelast SC-FDMA symbol of the subframe is also excluded. The referencesignal is used for coherent detection of a PUCCH. The PUCCH supports 7formats according to transmission information.

Table 1 shows the mapping relationship between PUCCH and UCI for use inLTE.

TABLE 1 PUCCH Format UCI Format 1 Scheduling request (SR) Format 1a1-bit HARQ ACK/NACK with/without SR Format 1b 2-bit HARQ ACK/NACKwith/without SR Format 2 CQI (20 coded bits) Format 2 CQI and 1- or2-bit HARQ ACK/NACK for extended CP Format 2a CQI and 1-bit HARQACK/NACK Format 2b CQI and 2-bit HARQ ACK/NACK

2. Channel Quality Indicator (CQI)

(1) CQI Overview

For efficient communication, it is desirable for network entities tofeed back channel information to each other. For example, DL channelinformation is fed back to UL and UL channel information to DL. Suchchannel information is referred to as CQI.

The CQI may be generated by various methods. For example, the CQI may begenerated as information quantizing a channel state itself, asinformation calculating a Signal-to-Interference plus Noise Ratio(SINR), or as information indicating a state to which a channel isactually applied, such as a Modulation Coding Scheme (MCS).

Hereinafter, a method for generating a CQI based on MCS information,e.g., a CQI generation method for a transmission scheme of HSDPA etc. in3GPP will be described. The MCS information includes information about amodulation scheme, a coding scheme, and a coding rate according to themodulation scheme and the coding scheme. Therefore, when a CQI isgenerated based on an MCS, if the modulation scheme and/or the codingscheme are changed, the CQI should vary according thereto. That is, atleast one CQI is needed per codeword.

In addition, if a MIMO system is applied to a network, the number ofnecessary CQIs is also changed. Because the MIMO system generatesmultiple channels using multiple antennas, plural codewords are usable.Accordingly, the number of CQIs is desirably increased as the number ofcodewords is increased. Notably, when the number of CQIs is increased,the amount of control information to be transmitted by network entitiesis proportionally increased.

FIG. 5 is a diagram illustrating one of UL CQI transmission methods.

A UE may measure DL channel quality while monitoring a DL channel andreport a selected CQI value based on the measured channel quality to aBS through a UL control channel. The BS performs DL scheduling (e.g. UEselection, resource allocation, etc.) according to the reported CQIvalue.

The CQI value may be set as an SINR, Carrier-to-Interference plus NoiseRatio (CINR), Bit Error Rate (BER), and/or Frame Error Rate (FER) of achannel and a value converted into transmittable data. In a MIMO system,feedback information including RI, PMI, etc. may be added to the CQIvalue as information indicating a channel state.

(2) Frequency Band Characteristics of CQI

A link adaptation scheme may be used to maximally use the channelcapacity of a radio channel in a wireless access system. The linkadaptation scheme refers to a scheme for adjusting an MCS and atransmission power according to a given channel. To use the linkadaptation scheme in a BS, CQI information needs to be fed back to theBS from a UE.

If a frequency band used in a network exceeds a coherence bandwidth, achannel abruptly varies in one bandwidth. A multicarrier system such asan OFDM system includes multiple subcarriers in a given bandwidth. Inthis case, since a modulated symbol is transmitted through eachsubcarrier, a channel signal may be transmitted per subcarrier tooptimally transmit the channel signal. However, in the multicarriersystem including a plurality of subcarriers, since channel informationshould be fed back every subcarrier, feedback channel information (e.g.control signals) may be abruptly increased. Accordingly, embodiments ofthe present invention propose various CQI generation methods forreducing control signal overhead.

(3) CQI Generation Method

Various CQI generation methods for reducing the amount of CQIinformation which is correspondingly increased as the transmissionamount of channel signals is increased will now be described.

1) The first method is to change the unit of channel informationtransmission. For example, multiple subcarriers may be integrated intoone subcarrier group and CQI information may be transmitted on a groupbasis. Namely, if 12 subcarriers are formed as one subcarrier group inan OFDM system using 2048 subcarriers, a total of 171 subcarrier groupsis formed. Accordingly, the amount of actually transmitted channelinformation is reduced to 171 from 2048.

In embodiments of the present invention, a basic unit of a method forintegrating one or more subcarriers into one group and reporting a CQIin the unit of a subcarrier group is defined as a CQI subcarrier groupor a CQI subband. In addition, if frequency bands do not distinguishbetween subcarriers, the whole frequency band may be divided intopartial frequency bands and a CQI may be generated based on the dividedfrequency bands. In this case, the divided frequency bands for CQIgeneration may be defined as CQI subbands.

2) Second, a CQI may be generated by compressing channel information.For example, this method compresses channel information in eachsubcarrier using a compression scheme in an OFDM scheme and transmitsthe compressed channel information. Schemes such as Discrete CosineTransform (DCT) may be considered as the compression scheme.

3) Third, a specific frequency band may be selected to generate channelinformation and a CQI for the selected specific frequency band may begenerated. For example, this method includes a best-M scheme in which anarbitrary number of best subcarriers (e.g. M subcarriers) is selectedfrom among subcarriers or subcarrier groups and then transmitted,instead of transmitting channel information in all subcarriers as in anOFDM system. When the CQI is generated and transmitted by selecting afrequency band, actually transmitted channel information may be broadlydivided into two parts: one is a CQI value and the other is a CQI index.

(4) Frequency Band Selective CQI Generation Method

A method for generating and transmitting a frequency band selective CQIwill be described hereinbelow.

FIG. 6 is a diagram illustrating frequency band selective CQI generationmethods.

The frequency hand selective CQI generation methods broadly includethree methods. The first method is to select a frequency band (i.e. CQIsubband) for generating a CQI. The second method is to generate andtransmit control information by manipulating CQI values of selectedfrequency bands. The third method is to transmit indexes of selectedfrequency bands (i.e. CQI subbands).

FIG. 6 shows the CQI subband selection method including i) a best-Mscheme, and ii) a threshold based selection scheme. In the best-Mscheme, network entities select M best CQI subbands having a goodchannel state. FIG. 6 shows the case where 3 best CQI subbands having agood channel state (i.e. a high CQI value) are selected from amongsubbands. Referring to FIG. 6, 3 subbands having a high CQI value, i.e.subbands of CQI indexes 5, 6, and 9 may be selected.

In the threshold based scheme, CQI subbands having a channel state valuehigher than a predetermined threshold value are selected. For example,in FIG. 6, a user may select CQI subbands having a CQI value higher thanthe threshold value, i.e. CQI subbands of indexes 5 and 6.

Meanwhile, the second method for generating control information bymanipulating CQI values includes iii) an individual transmission scheme,and iv) an average transmission scheme. In the individual transmissionscheme, all CQI values of CQI subbands selected from the above method i)are individually transmitted. In the individual transmission scheme, ifthe number of selected CQI subbands is increased, the number of CQIvalues to be transmitted is correspondingly increased.

In the average transmission scheme, an average value of CQI values ofselected CQI subbands is transmitted. Accordingly, the averagetransmission scheme has the advantage of transmitting only one CQI valueirrespective of the number of selected CQI subbands. Nonetheless,accuracy of a CQI value in each subband is lowered because the averageof multiple CQI subbands is transmitted. The average transmission methodmay use a simple arithmetic average or the average of CQI valuesconsidering channel capacity.

Moreover, the method for transmitting an index of a CQI subband includesv) a bitmap index scheme, and vi) a combinatorial index scheme. In thebitmap index method, one bit is allocated to each of all CQI subbands.If a CQI subband is selected, a bit of the CQI subband is set to ‘1’and, otherwise, it is set to ‘0’. Through the bitmap index scheme, whichCQI subband is used is easily indicated. However, the bitmap indexscheme should use a constant number of bits regardless of how many CQIsubbands are used.

In the combinatorial index scheme, how many CQI bands are to be used ispredetermined and combinations corresponding to the number of used CQIsubbands among all CQI subbands are mapped to indexes. For example, if atotal of N CQI subbands is present and M CQI subband indexes among the NCQI subbands are used, the total number of possible combinations isindicated by the following Equation 1.

$\begin{matrix}{{{}_{}^{}{}_{}^{}} = \frac{N!}{{\left( {N - M} \right)!}{M!}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

The number of bits indicating the number of cases derived from Equation1 may be obtained by the following Equation 2.

$\begin{matrix}{\left\lceil {\log_{2}\left( {{}_{}^{}{}_{}^{}} \right)} \right\rceil = \left\lceil {\log_{2}\left( \frac{N!}{{\left( {N - M} \right)!}{M!}} \right)} \right\rceil} & {{Equation}\mspace{14mu} 2}\end{matrix}$

Referring to FIG. 6, the total number of CQI subbands is 11. If Equation1 and Equation 2 are used to select three CQIs, then ₁₁C₃=165 and thenumber of bits indicating 165 cases is 8 (2⁷≦₁₁C₃≦2⁸).

(5) CQI Transmission Amount Increase Method

The number of CQIs transmitted by network entities may increaseaccording to various dimensions. First, a CQI increase in a spatialdomain will now be described. If a plurality of codewords is transmittedthrough a plurality of layers in a MIMO system, multiple CQIs are neededaccording to the codewords.

For example, a maximum of two codewords may be used in MIMO of a 3GPPLTE system and, in this case, two CQIs are needed. If one CQI iscomprised of 4 bits and two codewords are present, the CQI should becomprised of a total of 8 bits. Since all users transmit such a CQI toindicate a channel state, overhead caused by the CQI is abruptlyincreased in terms of radio resources. Accordingly, it is desirable toreduce the size of CQI information bits in terms of channel capacity.

A CQI increase in a frequency domain will now be described. If areceiver selects a frequency band of the best channel state andtransmits only the selected frequency and if a transmitter provides aservice only through the selected frequency band, a CQI is required inonly one band. Although such a scheme is suitable for a single userenvironment, it is not suitable for a multiuser environment because thefrequency having the best channel state cannot be allocated to allusers.

Problems occurring during a scheduling process when the CQI istransmitted in only one preferred band are as follows. If frequencybands preferred by multiple users do not overlap, there is no problem.However, simultaneous selection of a specific frequency band by multipleusers as the best channel environment is problematic.

Namely, users other than selected users cannot use the correspondingfrequency band. If each user transmits only one preferred frequencyband, there is no way to provide a service to the unselected users. Tosolve the above problem and effectively obtain multiuser diversity gain,CQI transmission for multiple frequency bands is required.

When CQIs corresponding to multiple frequency bands are transmitted, theamount of CQI transmission information is increased as many as selectedfrequency bands. For example, if users select three frequency bands inorder of a good channel state and transmit respective CQIs and frequencyband indicators, the transmission amount of CQIs increases by threetimes. Further, additional indicators need to be transmitted to indicatethe frequency bands selected by the users.

In addition, CQIs in both spatial and frequency domains may beconsidered. Multiple CQIs may be needed in the spatial domain andmultiple CQIs may be needed in the frequency domain.

Furthermore, a CQI increase in other dimensions may be considered. Forexample, if a Code Division Multiple Access (CDMA) scheme is used,signal strength and interference amount for each spread codeword arechanged. Hence, CQIs may be transmitted and received according to eachspread codeword and the number of CQIs may be increased in a codeworddimension.

To reduce the transmission amount of CQIs which is increased accordingto each domain, the concept of a differential CQI may be introduced. Forinstance, a user may normally transmit one CQI and transmit only adifference value between the one CQI and the other CQIs, therebyreducing the amount of CQI information. The differential CQI may beunderstood as a similar concept to differential modulation in amodulation/demodulation scheme. For example, if a plurality of CQIs isexpressed in a differential scheme, a large number of bits may beallocated as a CQI reference value and a relatively small number of bitsmay be allocated as a differential value, thereby reducing thetransmission amount of CQIs.

(6) CQI Transmission Mode

A UL channel used for CQI transmission in a 3GPP LIE system is shown inTable 2 below.

TABLE 2 Periodic CQI Aperiodic CQI Scheduling Scheme TransmissionTransmission Frequency non-selective PUCCH Frequency selective PUCCHPUSCH

Referring to Table 2, a CQI may be transmitted using a PUCCH at a perioddetermined in a higher layer or may be aperiodically transmitted using aPUSCH according to the necessity of a scheduler. The CQI can betransmitted using the PUSCH only in case of a frequency selectivescheduling scheme and aperiodic CQI transmission. Hereinafter, a CQItransmission method according to a scheduling scheme and periodicitywill be described.

1) CQI/PMI/RI Transmission Through PUSCH After Receiving CQITransmission Request Control Signal (CQI Request)

A control signal for requesting CQI transmission may be included in aPUSCH scheduling control signal (UL grant) transmitted through a PDCCH.The following Table 3 shows a UE mode when a CQI, a PMI, and an RI aretransmitted through the PUSCH.

TABLE 3 PMI Feedback Type No Single Multiple PMI PMI PMIs PUSCH CQIWideband Mode 1-2 Feedback (wideband CQI) UE selected Mode 2-0 Mode 2-2(subband CQI) Type Higher layer Mode 3-0 Mode 3-1 configured (subbandCQI)

The transmission mode of Table 3 is selected in a higher layer and theCQI/PMI/RI are transmitted in the same PUSCH subframe. Hereinafter, a ULtransmission method of a UE according to each mode will be described.

Mode 1-2 indicates the case of selecting a precoding matrix under theassumption that data for each subband is transmitted only through thesubband. A UE generates a CQI under the assumption of a selectedprecoding matrix with respect to a system band or a designated band (setS) in a higher layer. In Mode 1-2, the UE may transmit a CQI and a PMIvalue of each subband. In this case, the size of each subband may differaccording to the size of the system band.

A UE in Mode 2-0 may select M preferred subbands with respect to asystem band or a set S designated in a higher layer. The UE may generateone CQI value under the assumption that data is transmitted with respectto the M selected subbands. Additionally, the UE desirably reports oneCQI (wideband CQI) value with respect to the system band or the set S.If multiple codewords are present with respect to the M selectedsubbands, the UE defines CQI values for the respective codewords as adifferential format.

At this time, the differential CQI value is determined by a differencevalue between an index corresponding to a CQI value for the M selectedsubbands and an index of a wideband CQI.

The UE in Mode 2-0 may transmit information about locations of the Mselected subbands, one CQI value for the M selected subbands, and a CQIvalue generated for all bands or a designated band (set S) to a BS. Inthis case, the size of a subband and the M value may differ according tothe size of a system band.

A UE in Mode 2-2 may simultaneously select the locations of M preferredsubbands and a single precoding matrix for the M preferred subbandsunder the assumption that data is transmitted through the M preferredsubbands. A CQI value for the M preferred subbands is defined withrespect to each codeword. Moreover, the UE additionally generates awideband CQI value for a system band or a designated band (set S).

A UE in Mode 2-2 may transmit information about the locations of Mpreferred subbands, one CQI value for the M selected subbands, one PMIfor the M selected subbands, a wideband PMI, and a wideband CQI value toa BS. In this case, the size of a subband and the M value may differaccording to the size of a system band.

A UE in Mode 3-0 generates a wideband CQI value. The UE generates a CQIvalue for each subband under the assumption that data is transmittedthrough each subband. Even if RI>1, the CQI value indicates only a CQIvalue for the first codeword.

A UE in Mode 3-1 generates a single precoding matrix with respect to asystem band or a designated band (set S). The UE generates a subband CQIper codeword under the assumption of the above generated singleprecoding matrix with respect to each subband. The UE may also generatea wideband CQI under the assumption of a single precoding matrix. A CQIvalue of each subband may be expressed in a differential format. Asubband CQI value is calculated by the difference between a subband CQIindex and a wideband CQI index. The size of a subband may differaccording to the size of a system band.

2) Periodic CQI/PMI/RI Transmission Through PUCCH

A UE may periodically transmit a control signal (e.g. CQI/PMI/RIinformation) to a BS through a PUCCH. Upon receiving a control signalcommanding transmission of user data, the UE may transmit a CQI to theBS through a PUSCH. Even though the control signal is transmittedthrough the PUSCH, CQI/PMI/RI may be transmitted by one scheme amongmodes defined in the following Table 4.

TABLE 4 PMI Feedback Type No Single PMI PMI PUCCH CQI Wideband Mode 1-0Mode 1-1 Feedback (wideband CQI) Type UE selected Mode 2-0 Mode 2-1(subband CQI)

The UE may have a transmission mode as shown in Table 4. Referring toTable 4, in Mode 2-0 and Mode 2-1, a Bandwidth Part (BP) is a set ofsubbands contiguously located in a frequency domain and may cover both asystem band and a designated band (set S). In Table 4, the size of eachsubband, the size of a BP, and the number of BPs may vary with the sizeof a system band. The UE transmits a CQI per BP in the frequency domainin an ascending order so as to cover the system band or the designatedband (set S).

The UE may have the following four transmission types according totransmission combinations of CQI/PMI/RI.

i) First type (Type 1): A subband CQI (SB-CQI) of Mode 2-0 and Mode 2-1is transmitted.

ii) Second type (Type 2): A wideband CQI and PMI (WB-CQI/PMI) aretransmitted.

iii) Third type (Type 3): An RI is transmitted.

iv) Fourth type (Type 4): A wideband CQI is transmitted.

When the UE transmits an RI and a CQI/PMI, the RI and the CQI/PMI aretransmitted in subframes having different periods and offsets. If boththe RI and the CQI/PMI should be transmitted in the same subframe, theCQI/PMI is not transmitted.

In Table 4, a transmission period of a wideband CQI/PMI and a subbandCQI is P and the CQI/PMI and subband CQI have the followingcharacteristics.

The wideband CQI/PMI has a period of H*P where H=J*K+1, J denotes thenumber of BPs, and K denotes the number of all cycles of BPs. Namely,the UE transmits the wideband CQI/PMI at {0, H, 2H, . . . }.

The subband CQI is transmitted at a time J*K other than a time fortransmitting the wideband CQI/PMI.

In Table 4, the transmission period of the RI is M times the period ofthe wideband CQI/PMI and the RI and wideband CQI/PMI have the followingcharacteristics.

The offset of the RI and wideband CQI/PMI is O. If the RI and thewideband CQI/PMI are transmitted in the same subframe, the widebandCQI/PMI is not transmitted.

Parameters P, H, K, and O described above are determined by a higherlayer and are signaled to a physical layer of the UE.

Hereinafter, a feedback operation according to a UE mode will bedescribed. If the UE is in Mode 1-0 and transmits an RI to the BS, theUE generates the RI with respect to a system band or a designated band(set S) and transmits a third type report for transmitting the RI to theBS. In the case of CQI transmission, the UE transmits a wideband CQI.

If the UE is in Mode 1-1 and transmits an RI to the BS, the UE generatesthe RI with respect to a system band or a designated band (set S) andtransmits the third type report for transmitting the RI to the BS.During transmission of CQI/PMI, the UE selects a single precoding matrixin consideration of a latest transmitted RI. That is, the UE transmits asecond type report including a wideband CQI, a single precoding matrix,and a differential wideband CQI to the BS.

If the UE is in Mode 2-0 and transmits an RI, the UE generates the RIwith respect to a system band or a designated band (set S) and transmitsthe third type report for transmitting the RI to the BS. Duringtransmission of a wideband CQI, the UE generates the wideband CQI underthe assumption of a latest transmitted RI and transmits a fourth typereport to the BS. Upon transmitting a CQI for a selected subband, the UEselects the most preferred subband with respect to J BPs including Nsubbands and transmits a first type report to the BS. The first typereport may be transmitted through one or more subframes according to aBP.

If the UE is in Mode 2-1 and transmits an RI, the UE generates the RIwith respect to a system band or a designated band (set S) and transmitsthe third type report for transmitting the RI to the BS. Duringtransmission of a wideband CQI, the UE generates the wideband CQI underthe assumption of a latest transmitted RI and transmits the fourth typereport to the BS. In case of a CQI for selected subbands is transmitted,the UE generates a single CQI value for subbands selected in BPs inconsideration of a latest transmitted PMI/RI with respect to j BPsincluding Nj subbands and a CQI difference between codewords under theassumption that the latest transmitted RI and a single precoding matrixfor the selected subbands are used when the RI is greater than 1 andtransmits the first type report to the BS.

3. Multicarrier Environment

A communication environment considered in the embodiments of the presentinvention includes a multicarrier support environment. That is, amulticarrier system or a carrier aggregation system used in the presentinvention refers to a system configuring a wideband by aggregating morethan one carrier having a bandwidth narrower than a target bandwidth forwideband support.

In the present invention, multicarrier refers to carrier aggregation andcarrier aggregation includes non-contiguous carrier aggregation as wellas contiguous carrier aggregation. In addition, the term carrieraggregation is used interchangeably with the term bandwidth aggregationetc.

In an LTE-A system, multicarrier (i.e. carrier aggregation) configuredby combining two or more CCs is designed for supporting up to 100 MHz.When one or more carriers having a narrower bandwidth than a targetbandwidth are aggregated, the bandwidth of the aggregated carriers maybe limited to a bandwidth used in a legacy system in order to maintainbackward compatibility with a legacy IMT system.

For example, a 3GPP LTE system (LIE R-8 system) may support bandwidthsof {1.4, 3, 5, 10, 15, 20} MHz and a 3GPP LTE-Advanced system (i.e.LIE-A system) may support a bandwidth wider than 20 MHz using the abovebandwidths supported by the LTE system. In addition, a multicarriersystem used in the present invention may define a new bandwidthirrespective of a bandwidth used in a legacy system to support carrieraggregation.

FIG. 7, including (a) and (b), is a diagram illustrating an example of aCC used in an LTE system and multiple carriers (carrier aggregation)used in an LTE-A system.

FIG. 7( a) shows a single carrier structure used in the LTE system. A CCincludes a DL CC and a UL CC. One CC may have a frequency range of 20MHz.

FIG. 7( b) shows a multicarrier structure used in the LTE-A system. Inthe illustrated case of FIG. 7( b), three CCs each having a frequencybandwidth of 20 MHz are aggregated. In multicarrier aggregation, a UEmay simultaneously monitor three CCs and may receive DL signal/data ortransmit UL signal/data.

If N DL CCs are managed in a specific e-NodeB (eNB), a network mayallocate M (M≦N) DL CCs to a UE. The UE may monitor only the M limitedDL CCs and receive a DL signal. The network may allocate L (L≦M≦N) DLCCs to the UE according to priority. In this case, the UE shouldnecessarily monitor the L DL CCs. This scheme may also be applied to ULtransmission.

The LTE-A system uses the concept of a cell to manage radio resources.The cell is defined as a combination of a DL resource and a UL resourceand the UL resource may be selectively defined. For example, the cellmay be configured by the DL resource alone or by the DL resource and theUL resource. When multicarrier (i.e. carrier aggregation) is supported,the linkage between the carrier frequency of the DL resource (or DL CC)and the carrier frequency of the UL resource (or UL CC) may be indicatedby system information. Namely, one cell is comprised of one or more DLCCs and may selectively include one or more UL CCs.

The concept of a cell used in the LTE-A system includes a Primary cell(PCell) and a Secondary cell (SCell). The PCell may refer to a celloperating on a primary frequency (or primary CC) and the SCell may referto a cell operating on a secondary frequency (or secondary CC). Notably,only one PCell and one or more SCells may be allocated to a specific UE.

The PCell is used to perform an initial connection establishmentprocedure or a connection re-establishment procedure. The PCell mayrefer to a cell indicated during a handover procedure. The Scell can beconfigured after RRC_CONNECTED is established and may be used to provideadditional radio resources.

The PCell and SCell may be used as a serving cell. In the case of a UEin which carrier aggregation is not configured or carrier aggregation isnot supported even in an RRC_CONNECTED state, only a single serving cellcomprised of only a PCell is present. Meanwhile, in the case of a UE inwhich carrier aggregation is configured in an RRC_CONNECTED state, oneor more serving cells may be present and all cells include a PCell andone or more Scells.

After an initial security activation procedure is started, an E-UTRANmay configure a network including one or more SCells in addition to aninitially configured PCell during a connection establishment procedure.In a multicarrier environment, each of a PCell and an SCell may serve asa CC. Namely, carrier aggregation may be understood as a combination ofa PCell and one or more SCells. In the following embodiments, a PrimaryCC (PCC) may have the same meaning as a PCell and a Secondary CC (SCC)may have the same meaning as an SCell.

FIG. 8 is a diagram illustrating an exemplary cross-CC scheduling methodwhich can be used in the present invention.

A PDCCH structure and DCI format defined in LTE Rel-8 specification donot support cross-CC scheduling. In other words, the DCI format andPDCCH transmission structure (the same coding method and the same CCEbased resource mapping) of LTE Rel-8 are used. For example, a PDCCH on aCC allocates PDSCH resources to the same CC and allocates PUSCHresources to a linked UL CC. In this case, a Carrier Indicator Field(CIF) is not necessary. In addition, related PDSCH transmission and ULA/N, PUSCH transmission, and PHICH transmission methods conform to LIERel-8 specification.

A PDCCH structure and DCI format defined in L E-A specification maysupport cross-CC scheduling. That is, a PDCCH (DL grant) and a PDSCH maybe transmitted on different DL CCs or a PUSCH transmitted according to aPDCCH (UL grant) transmitted on a DL CC may be transmitted through a ULCC other than a UL CC linked with the DL CC receiving the UL grant.

In this case, a PDCCH requires a CIF indicating through which DL/UL CC aPDSCH/PUSCH indicated by the PDCCH is transmitted. For example, thePDCCH may allocate a PDSCH or PUSCH resource to one of a plurality ofCCs using a CIF. To this end, a DCI format of the LTE-A system may beextended according to a 1-bit or 3-bit CIF and may reuse the PDCCHstructure of LTE Rel-8.

Whether cross-CC scheduling is permitted may be determinedUE-specifically, UE-group specifically, or cell-specifically. Signalingoverhead can be reduced by semi-statically toggling operation ofcross-CC operation.

In this way, the size of a CIF according to permission/non-permission ofcross-CC scheduling, i.e. activation/deactivation of cross-CC schedulingmay be semi-statically set. This is similar to the case in which a UEspecific transmission mode is semi-statically determined in LTE Rel-8.However, the size of a CIF may be fixed at 3 bits according to acommunication environment and the location of the CIF may be fixedregardless of the size of a DCI format.

If cross-CC scheduling is deactivated, this means that a PDCCHmonitoring set is always the same as a UE DL CC set. In this case, anindication such as additional signaling for the PDCCH monitoring set isnot necessary. If cross-CC scheduling is activated, the PDCCH monitoringset is desirably defined in the UE DL CC set and, at this time, anindication such as additional signaling for the PDCCH monitoring set isnecessary.

When a CIF is present, an eNB may allocate a DL CC set for monitoringPDCCHs in order to reduce the number of blinding decoding operations ofa UE. The DL CC set may be a part of all aggregated DL CCs and the UEcan detect and decode the PDCCHs only in the allocated DL CC set. Thatis, the eNB can transmit PDCCHs only through the DL CC monitoring set toschedule the PDSCH and PUSCH for the UE. The PDCCH DL CC monitoring setmay be configured UE-specifically, UE group-specifically, orcell-specifically.

Referring to FIG. 8, for example, three DL CCs are aggregated in a DLsubframe with respect to an LTE-A UE. DL CC A may include a PDCCHmonitoring DL CC. If a CIF is disabled, a PDCCH and a PDSCH aretransmitted through the same DL CC scheduled according to an LTE Rel-8rule. If the CIF is enabled, the PDCCH may be transmitted through themonitoring DL CC A and the PDSCH may be transmitted through DL CC B andDL CC C as well as DL CC A. Notably, the PDCCH cannot be transmittedthrough DL CC B and DL CC C other than the DL CC monitoring set.

4. CSI Transmission Method for Multiple Serving Cells

Hereinafter, a CSI transmission method for multiple cells as anembodiment of the present invention will be described in detail.

If two or more serving cells are allocated to a UE, the UE may besemi-statically configured by a higher layer so as to periodicallyfeedback CSI on a PUCCH. The CSI may include a CQI, a PMI, an RI, and/ora Precoding Type Indicator (PTI).

In an LTE Ranjdiel-8 system, a CSI type transmitted from the UE isclassified into an RI, a wideband CQI (WB-CQI)/PMI, and a subband CQI(SB-CQI) as shown in Table 5. Table 5 shows CSI types transmitted by theUE in the LTE-A system according to each case. Order of CQI transmissionperiods according to each type is RI>WB-CQI/PMI>SB-CQI.

TABLE 5 LTE-A LTE Rel-8 Case #1 Case #2 Case #3 Case #4 Case #5 Case #6Case #7 Case #8 CSI RI RI L-PMI RI/L-PMI RI L-PMI RI/L-PMI RI L-PMI Type1 CSI WB- L-PMI RI WB- L-PMI RI WB-CQI WB- WB- Type 2 CQI/PMI CQI/S-CQI/L-PMI CQI/RI PMI CSI SB-CQI WB- WB- SB-CQI WB-CQI WB-CQI SB-SB-CQI/S- SB- Type 3 CQI/S- CQI/S- CQI/S- PMI CQI/S- PMI PMI PMI PMI CSISB-CQI SB-CQI SB- SB- Type 4 CQI/S- CQI/S- PMI PMI

Referring to Table 5, the present invention may use a Long-term (L-PMI)and a Short-term PMI (S-PMI) in order to improve performance throughCooperative Multi-Point (CoMP) between cells considering more precisechannel adaptation than in LTE Rel-8 and intercell interference. It isassumed that the transmission period of the L-PMI is longer than thetransmission period of the S-PMI. The L-PMI may be referred to as afirst PMI and the S-PMI may be referred to as a second PMI.

The CSI type for LTE-A considering the L-PMI and S-PMI may be appliedbased on a specific case among the possible cases proposed in Table 5.In Table 5, a transmission period of N type CSI is longer than atransmission period of N+1 type CSI. It is assumed in the presentinvention that the N type CSI has higher priority than the N+1 type CSI.Namely, high priority may be allocated to CSI having a long transmissionperiod. It is also assumed that the CSI type and the number of CSI forCSI transmission of each DL CC based on a specific case areindependently configured according to each DL CC. Hereinafter, adescription will be given under the assumption that Case #1 in Table 5is applied for convenience of description.

Since a plurality of CCs is aggregated in an LTE-A system, CSI for theplurality of CCs needs to be transmitted to an eNB from a UE. That is,the UE should transmit CSI for one or more serving cells to the eNB.When the UE considers periodic CSI transmission through a controlchannel (e.g. PUCCH), configuration information for CSI transmission ofthe multiple DL CCs, (e.g. a CSI transmission period, CSI transmissionmode, and/or a CSI type), may be identically set with respect to allserving cells (e.g. DL CCs) or each serving cell group or may beindependently set with respect to each serving cell. Also, PUCCH indexesfor CSI transmission of multiple serving cells may be identically setwith respect to all serving cells or each serving cell group or may beindependently set with respect to each serving cell.

In order to reduce distortion of a power amplifier during ULtransmission of a UE in addition to Rel-8 and LTE-A systems, a singlecarrier property needs to be maintained with respect to a ULtransmission signal. To this end, it is necessary to define a UEbehavior for maintaining a single carrier property of a UL transmissionsignal when a plurality of PUCCHs should be transmitted through the samesubframe.

Hereinafter, a UE UL behavior for CSI transmission for multiple servingcells (DL CCs) in a multicarrier aggregation environment will bedescribed. For example, a method for transmitting one piece of controlinformation (i.e. CSI) through one PUCCH is provided when CSItransmission for a plurality of DL CCs is simultaneously needed througha plurality of PUCCHs or PUSCHs in a specific subframe. In addition, aCSI drop method according to CSI priority is disclosed so that onlyspecific CSI among plural pieces of CSI can be transmitted. For example,a method for dropping a CQI for each serving cell according to servingcell type, CSI transmission period, and/or CSI type is described inaccordance with embodiments of the present invention.

In the embodiments of the present invention, the term CC is usedinterchangeably with the term cell as described earlier. In other words,a serving cell basically includes one or more DL CCs and, in some cases,includes UL CCs. In addition, one serving cell may include one DL CCand/or a UL CC.

FIG. 9 is a diagram illustrating a CSI report method according topriority of CSI in accordance with an embodiment of the presentinvention.

Hereinbelow, a method will be described for differently configuring thecontents of CSI for serving cells by independently configuring CSItransmission and feedback mode for each serving cell (e.g. DL CC)according to an embodiment of the present invention. Namely, thecontents of CSI may be comprised of one or more CSI reporting types. TheCSI reporting type may be generated in association with a PUCCH format.

An eNB controls time and frequency resources capable of being used forCSI reporting. According to the embodiments of the present invention,CSI may include one or more of a CQI, Mils (e.g., first PMI and a secondPMI), and an RI.

If one or more serving cells are allocated to a UE, the UE mayperiodically transmit CSI to all activated serving cells. The UE mayobtain information about CSI reporting modes for one or more servingcells through higher layer signaling. The UE may obtain one or moretransmission periods and offset values of the CQI, PMI, PTI, and RIthrough higher layer signaling (S910).

The UE may communicate with the eNB through one or more serving cellsand may monitor and measure states of DL channels (S920).

The UE may report CSI for one or more activated serving cells to the eNBat transmission periods according to the contents of the CSI. In otherwords, the UE transmits CSI of a first serving cell and CSI of a secondserving cell to the eNB at each CSI transmission period (S930 and S940).

If the UE is in a simultaneous transmission mode of PUSCH and PUCCHsignals in steps S930 and S940, the UE may periodically report eachpiece of CSI to the eNB through a PUCCH. If the UE is not in asimultaneous transmission mode of PUSCH and PUCCH signals, the UE mayperiodically report CSI to the eNB through a PUSCH by piggybacking theCSI on the PUSCH signal.

Notably, transmission periods of CSI may overlap in the same subframewhile the UE reports the CSI for each serving cell to the eNB. Namely,pieces of CSI to be transmitted in a specific subframe by the UE maycollide with each other (S950).

According to the embodiments of the present invention, if CSI reportsfor two or more serving cells overlap in the same subframe, CSI only forone serving cell may be transmitted. Accordingly, the UE may comparepriorities of CSI reporting types related to a PUCCH format (S960),select CSI having a high priority to report the CSI to the eNB, and dropCSI for the other cells (S970).

Priorities of CSI reporting types may be determined in consideration ofa cell type, a CSI reporting period, a CSI reporting type, a UEtransmission mode, CSI reporting mode, and/or a PUCCH format. In the CSIreporting type, transmission periods and offsets may be determinedaccording to a PUCCH CSI reporting mode.

The case in which the UE drops CSI according to priority of a CSIreporting type will be described below. The CSI reporting type indicatesCSI according to CSI reporting mode and is used to support the CSIreporting mode. It is assumed in Table 5 that CSI Type 1 has the highestpriority of a CSI reporting type and CSI Type 4 has the lowest priorityof a CSI reporting type.

Referring to Table 5, in Case #3, CSI Type 1 indicates that the UEreports an RI and a first PMI (L-PMI) to the eNB (i.e. CSI reportingtype 5). CSI Type 2 indicates that the UE reports a WB-CQI and a secondPMI (S-PMI) to the eNB (i.e. CSI reporting type 2b). CSI Type 3indicates that the UE reports an SB-CQI to the eNB (i.e. CSI reportingtype 1).

In Case #6, CSI Type 1 indicates that the UE reports an RI and a firstPMI (L-PMI) to the eNB (i.e. CSI reporting type 5). CSI Type 2 indicatesthat the UE reports a WB-CQI to the eNB (i.e. CSI reporting type 4). CSIType 3 indicates that the UE reports an SB-CQI and a second PMI (S-PMI)to the eNB (i.e. CSI reporting type 1a).

In Case #7, CSI Type 1 indicates that the UE reports an RI to the eNB(i.e. CSI reporting type 3). CSI Type 2 indicates that the UE reports aWB-CQI and a first PMI (L-PMI) to the eNB (i.e. CSI reporting type 2c).CSI Type 3 indicates that the UE reports an SB-CQI and a second PMI tothe eNB (i.e. CSI reporting type 1a). As to the contents of CSI reportsfor the other cases, reference is made to Table 5.

If the UE should simultaneously transmit CST Type 1 for a first servingcell and CSI Type 2 for a second serving cell in a predeterminedsubframe (i), the UE may drop CSI for CSI Type 2 having a lower priorityand report only CSI for CSI Type 1 to the eNB because the priority ofCSI Type 1 is higher than the priority of CSI Type 2.

If CSI of CSI Type 2 collides with CSI of CSI Type 3 in step S950, theUE may drop CSI for CSI Type 3 having a lower priority and report onlyCSI for CSI Type 2 to the eNB. Obviously, if CSI of CSI Type 1 collideswith CSI of CSI Type 3, the UE may report only CSI for CSI Type 1 to theeNB and drop CSI for CSI Type 3 (S950 to S970).

Priorities according to CSI reporting type in Table 5 are as follows. ACSI reporting type 3 or 5 has a higher priority than a CSI reportingtype 2b, 2c, or 4 and a CSI reporting type 2b, 2c, or 4 has a higherpriority than a CSI reporting type 1 or 1a.

Accordingly, if CSI of the CSI reporting type 3 or 5 collides with CSIof the CSI reporting type 2b, 2c, or 4 in the same subframe, the UEdrops the CSI of the CSI reporting type 2b, 2c, or 4 having a lowerpriority and transmits only the CSI of the CSI reporting type 3 or 5 tothe eNB. In addition, if CSI of the CSI reporting type 2b, 2c, or 4collides with CSI of the CSI reporting type 1 or 1a in the samesubframe, the UE drops the CSI of the CSI reporting type 1 or 1a havinga lower priority and transmits the CSI of the CSI reporting type 2b, 2c,or 4 to the eNB.

FIG. 10 is a diagram illustrating a CSI drop method according to celltype in accordance with an embodiment of the present invention.

If the UE needs to transmit CSI for a plurality of serving cells (i.e. aplurality of DL CCs) during the same time duration, the UE may transmitonly CSI for a PCell and may drop CSI for the other SCells according tocell type (i.e. CC type).

For stable system information transmission, control informationtransmission, and cross-CC scheduling, there is a high possibility thata serving cell having a good channel state among a plurality of servingcells is set as an anchor cell (i.e. anchor DL CC) or a PDCCH monitoringcell. In this case, the anchor cell or PDCCH monitoring cell may be setas a PCell. Moreover, DL data transmission may first be performedthrough the PCell.

In the embodiments of the present invention, a CSI report for the PCell(i.e. anchor DL CC or PDCCH monitoring DL CC) can be guaranteed first.In FIG. 9, DL CC #1 represents a PCell and DL CC #2 represents an SCell.It is assumed that transmission periods of CQI information such as RI,L-PMI, WB-CQI/S-PMI, and SB-CQI in the PCell are 40, 20, 10, and 5 ms,respectively and transmission periods of RI, L-PMI, WB-CQI/S-PMI, andSB-CQI in the SCell are 48, 24, 12, and 6 ms, respectively.

Referring to FIG. 10, transmission periods of CQIs of cells may overlap.In this case, the UE may transmit only CQI information for the PCell anddrop CQI information for the SCells, thereby maintaining a singlecarrier property.

FIG. 11 is a diagram illustrating a CSI drop method according to a CSIreporting period in accordance with an embodiment of the presentinvention.

If the UE needs to transmit CSI for a plurality of serving cells (i.e. aplurality of DL CCs) in the same subframe, the UE may drop CSI accordingto CSI transmission period. Namely, the UE may first report leastfrequently used CSI out of CSI reported to the eNB and drop CSI for theother cells transmitted in the same subframe.

If an interval of a transmission time duration of CSI is significantlyincreased, a channel adaptation result according to a UE mobility changecannot be reliable. Accordingly, CSI having a long transmission periodmay first be transmitted in consideration of the transmission period ofCSI.

For example, if CSI transmission for a plurality of serving cells issimultaneously needed in the same subframe, the UE may transmit only CSIfor a cell having the longest transmission period of a CSI reportingmode and drop CSI having a relatively short transmission period. As torelative magnitude of a transmission period according to CQI type,reference may be made to Table 5.

If CSI transmission for a plurality of serving cells is simultaneouslyneeded in the same subframe, the UE may transmit only CSI for a servingcell having the longest transmission period according to CSI reportingmodes to be transmitted in the same subframe.

It is assumed in FIG. 11 that a first serving cell (DL CC #1) is a PCelland a second serving cell (DL CC #2) is an SCell. It is also assumedthat transmission periods of CSI transmitted in the PCell and Scell arethe same as transmission periods described with reference to FIG. 10.The UE may transmit only CSI for a serving cell having the longesttransmission period according to CSI type and may drop the other CSI.

In FIG. 11, only CSI having the longest transmission period according toCSI type in Case #1 is transmitted. Referring to Table 5, thetransmission period is in order of RI>L-PMI>WB-CQI/S-PMI>SB-CQI. If thetransmission period of CQI information of the SCell is longer than thatof the PCell even though CQI information is CQI information in the PCell(e.g. SB<LP, LP<SP, and SP<SB), the UE may transmit CSI of the SCell anddrop CSI of the PCell.

Although the first serving cell is a PCell and the second serving cellis an SCell in FIG. 11, the first serving cell may be an SCell and thesecond serving cell may be a PCell.

FIG. 12 is a diagram illustrating a CSI drop method according to CSItype in accordance with an embodiment of the present invention.

If simultaneous transmission of two or more CSIs for a plurality ofserving cells is needed, the UE may drop CSI according to CSI type. CSIconfiguration may be independently set according to a serving cell (e.g.DL CC). Therefore, the numbers of CSI types, M, configured in respectivecells may be the same or different. For example, when Case #1 of Table 5is applied, all four CQI types of RI, L-PMI, WB-CQI/S-PMI, and SB-CQImay be set for a PCell (DL CC #1) and three CSI types of RI, L-PMI, andWB-CQI/S-PMI may be set for an SCell (DL CC #2). Hereinafter, a CSItransmission method of a UE will be described when the number of CSItypes, M, is the same.

In the embodiment of the present invention, a CSI type having a lowpriority (i.e. a short period) may be determined depending upon a CSItype having a high priority (i.e. long period). In other words, thepriority of CSI transmission may differ according to CSI type. Assumingthat Case #1 in Table 5 is applied, a rank (i.e. RI) is first determinedand then an L-PMI may be determined only in a long-term precodingcodebook. In this case, an S-PMI is determined in a short-term precodingcodebook specified (e.g. precoder-transformed or subset restricted) bythe determined L-PMI and a WB-CQI and an SB-CQI may be determineddepending on the S-PMI. Accordingly, determination of a CSI type havinga low priority is meaningful only when a CSI type having a high priorityis predetermined.

In FIG. 12, a method for first ensuring CSI transmission for a DL CChaving the highest priority of a CSI type is shown in consideration ofthe above description. It is assumed in FIG. 12 that the same number ofCSI types (i.e. M=4) is set for a PCell (DL CC #1) and an SCell (DL CC#2). It is also assumed that a transmission period of each CSI type isthe same as that described with reference to FIG. 10.

Referring to FIG. 12, if CSI report times for two serving cells (DL CC#1 and DL CC #2) are the same, the UE transmits only CSI for a cellhaving the highest priority of a CSI type to be transmitted in the samesubframe. Namely, if one or more serving cells are allocated to the UEand CSI for two or more serving cells should be transmitted in the samesubframe, the UE may transmit CSI only for a serving cell having a highpriority and drop CSI for the other cells.

For example, since first type CSI has a higher priority than other typesof CSI, the UE may transmit only the first type CSI and drop the otherCSI. Referring to FIG. 12, when an SB-CQI (SB) is transmitted in a PCelland an L-PMI (LP) is transmitted in an SCell in the same subframe, sincethe CSI type (#2) of the LP is lower than the CSI type (#4) of the SB inCase #1, the UE transmits only the LP and may drop the SB. In addition,since the CSI type of an SP (WB-CQI/S-PMI) is lower than the CSI type ofthe SB, the UE transmits only the SP and may drop the SB-CQI.

FIG. 13 is a diagram illustrating another CSI drop method according toCSI type in accordance with an embodiment of the present invention.

If simultaneous transmission of CSI for a plurality of serving cells isneeded, the UE may drop CSI according to CSI type. CSI may beindependently configured according to a serving cell (e.g. DL CC).Therefore, the numbers of CSI types, M, configured in respective cellsmay be the same or different. Hereinafter, a CSI transmission method ofa UE will be described when the numbers of CSI types, M, are thedifferent.

In FIG. 13, the number of CSI types for a PCell (DL CC #1), M, is 4 anda transmission period of each CSI type is the same as that in FIG. 10.Notably, the number of CSI types for an SCell (DL CC #2), M, is 3 andCSI includes RI, L-PMI, WB-CQI/S-PMI. It is assumed that transmissionperiods of RI, L-PMI, and WB-CQI/S-PMI in the SCell are 48, 24, and 12ms, respectively. In FIG. 13, the UE may transmit only CSI for a cellhaving a least number of CSI types. That is, since the number of CSItypes in the PCell is 4 and the number of CSI types in the SCell is 3,the UE may transmit only CQI information of the Scell when CSI of theScell and CSI of the PCell are transmitted in the same subframe.

In the illustrated case of FIG. 13, the UE transmits only CSI for aserving cell having a least number of CQI types to the eNB. However,even though M values are different, the UE may transmit specific CSIaccording to a priority of a CSI type and drop the other CSI asdescribed with reference to FIG. 12.

If an RI or L-PMI is included in a CSI type to be transmitted in thesame subframe, the UE may operate as shown in FIG. 12 and, otherwise,the UE may transmit only CSI for a serving cell having the smallest Mvalue as shown in FIG. 13.

Alternatively, the UE may transmit only CSI for a serving cell havingthe largest M value as opposed to FIG. 13. In this case, the UE maytransmit only CSI of the PCell in FIG. 13.

If an RI or L-PMI is included in a CSI type to be transmitted in thesame subframe, the UE may operate as shown in FIG. 12 and, otherwise,the UE may transmit only CSI for a serving cell having the largest Mvalue.

Therefore, when M values are different, a CSI drop method may beselectively applied according to activation/deactivation offrequency-selective scheduling and dependency for a serving cell. Inaddition, transmission for a CSI type having a high priority such as anRI or L-PMI can be guaranteed regardless of an M value.

5. PHICH Allocation Method

(1) PHICH Allocation Method in LTE Rel-8 System

In an LTE Rel-8 system, ACK/NACK feedback for UL data transmissionthrough a PUSCH is transmitted through a DL PHICH resource. MultiplePHICH resources are distinguished by a combination of time, frequency,orthogonal code including different cyclic shifts, and/or I/Q phasedomains. For transmission of each PUSCH signal, a PHICH resource usedfor ACK/NACK feedback corresponding to the PUSCH signal is determinedbased on a UL Resource Block (RB) of the first slot in which the PUSCHsignal is transmitted. That is, all indexes of UL RBs are linked withall PHICH resources. FIG. 14 is a diagram illustrating the linkagebetween 100 UL RBs and 100 DL PHICH resources.

For ACK/NACK transmission for PUCCH transmission, a PHICH resourcelinked with an index of a UL RB having the least frequency among UL RBsused for PUSCH transmission is used. Namely, a PHICH resource linkedwith a lowest RB index used for PUSCH transmission is selected forACK/NACK feedback. However, in an LTE Rel-8 system, there is nodefinition for the linkage between PHICH resources and the UL RBs addedby application of a carrier aggregation technique. Further, in apredefined linkage relationship between PHICH resources and UL RBS, aPHICH resource used for PUSCH transmission may be adjusted by an offsetvalue signaled by a higher layer and additional configuration.

(2) PHICH Allocation Method in LTE-A System

In the embodiment of the present invention, it is considered even in ULthat plural (e.g. two) non-contiguous frequency resources (e.g. RBs orRB groups) are allocated to one UE in order to raise frequency resourceusage efficiency, instead of allocating only contiguous frequencyresources to one UE.

A UE used in the present invention can support UL multi-antennatransmission (i.e. UL MIMO) for high-speed large-capacity datatransmission through UL and UL non-contiguous Resource Allocation (RA)can be applied during such UL MIMO transmission.

When two codewords (CWs) are transmitted through UL MIMO, the UErequires two PHICH resources (indexes) to transmit ACK/NACK for each CW.In the embodiments of the present invention, methods for allocating twoPHICH resources considering application of UL non-contiguous RA aredisclosed when the UE performs UL MIMO transmission.

FIGS. 15 to 19 are diagrams illustrating exemplary PHICH resourceallocation methods in accordance with embodiments of the presentinvention.

Referring to FIG. 15, if one RB is allocated to a UE for PUSCHtransmission, two PHICH resources linked to an allocated RB index (nRB)and an RB index (nRB+1) adjacent thereto may be allocated as ACK/NACKtransmission resources for 2-CW transmission.

FIG. 16 to FIG. 18 show the cases in which two or more RBs are allocatedto a UE for PUSCH transmission. Two PHICH resources linked to the lowestindex and the second lowest index among the allocated RB indexes may beallocated as ACK/NACK transmission. resources for 2-CW transmission.

In FIG. 16, a UL contiguous RA method is applied. A PHICH index mappedto the lowest RB index among UL RBs and a PHICH index adjacent theretomay be allocated as PHICH resources.

In FIG. 17 and FIG. 18, a UL non-contiguous RA method is applied. InFIG. 17, a PHICH index indicated by the lowest RB index amongnon-contiguous UL RBs and a PHICH index adjacent thereto may beallocated as PHICH resources. Meanwhile, in FIG. 18, a PHICH indexindicated by the lowest RB index from each of non-contiguous RB groupsmay be allocated as PHICH resources.

If a UL contiguous RA method is applied for PUSCH transmission of a UE,two PHICH resources linked to the lowest index nRB among allocated RBindexes and an RB index nRB+1 adjacent thereto may be allocated to theUE as ACK/NACK transmission resource for 2-CW transmission (refer toFIG. 15 and FIG. 16).

If UL non-contiguous RA is applied for PUSCH transmission of a UE (i.e.two non-contiguous RB groups are allocated), two PHICH resources linkedto the lowest indexes among RB indexes in the respective RB groups maybe allocated to the UE as ACK/NACK transmission resources for 2-CWtransmission (refer to FIG. 17 and FIG. 18).

FIG. 20 is a diagram illustrating an apparatus for supporting a CSItransmission method disclosed in the present invention in accordancewith an embodiment of the present invention.

A UE may operate as a transmitter in UL and as a receiver in DL. An eNBmay operate as a receiver in UE and as a transmitter in DL.

The UE and eNB may include Transmit (Tx) modules 2040 and 2050 andReceive (Rx) modules 2050 and 2070, respectively, for controllingtransmission and reception of information, data, and/or messages, andmay include antennas 2000 and 2010, respectively, for transmitting andreceiving the information, data, and/or messages. The UE and eNB mayinclude processors 2020 and 2030 for performing the embodiments of thepresent invention and memories 2080 and 2090 for temporarily orpermanently storing processing procedure performed by the processors,respectively.

Especially, the processors 2020 and 2030 may measure and report thestate of a DL channel for each serving cell activated in a carrieraggregation environment described in the embodiments of the presentinvention. The processors may also report CSI to the eNB depending on aCSI priority according to a CSI reporting type (or priority according toa PUCCH format). For example, if CSI for one or more serving cellsshould be transmitted in the same subframe according to each CSItransmission period, the processor of the UE compares priorities for theCSI and may transmit only CSI having a higher priority to the eNB.

The Tx modules and Rx modules included in the UE and the eNB may performa packet modulation/demodulation function for data transmission, a quickpacket channel coding function, Orthogonal Frequency Division MultipleAccess (OFDMA) packet scheduling, Time Division Duplex (TDD) packetscheduling, and/or a channel multiplexing function. The UE and eNB ofFIG. 20 may further include a low-power Radio Frequency(RF)/Intermediate Frequency (IF) module.

The apparatus described in FIG. 20 is a means for implementing the CSIreporting methods described in the embodiments of the present invention.The embodiments of the present invention may be performed usingconstituent elements and functions of the aforementioned UE and eNB.

Meanwhile, the UE in the present invention may be any of a PersonalDigital Assistant (PDA), a cellular phone, a Personal CommunicationService (PCS) phone, a Global system for Mobile (GSM) phone, a WidebandCDMA (WCDMA) phone, a Mobile Broadband System (MBS) phone, a hand-heldPC, a notebook PC, a smart phone, a Multi Mode-Multi Band (MM-MB)terminal, etc.

The smart phone is a terminal having the advantages of both a mobilecommunication terminal and a PDA and may refer to a terminal in whichdata communication functions such as scheduling management, faxtransmission and reception, and Internet access, which are functions ofthe PDA, are incorporated into the mobile communication terminal. TheMM-MB terminal refers to a terminal which has a multi-modem chip thereinand which can operate in any of a mobile Internet system and othermobile communication systems (e.g., a CDMA2000 system, a WCDMA, etc.).

The embodiments of the present invention may be achieved by variousmeans, for example, hardware, firmware, software, or a combinationthereof.

In a hardware configuration, the exemplary embodiments of the presentinvention may be achieved by one or more Application Specific IntegratedCircuits (ASICs), Digital Signal Processors (DSPs), Digital SignalProcessing Devices (DSPDs), Programmable Logic Devices (PLDs), FieldProgrammable Gate Arrays (FPGAs), processors, controllers,microcontrollers, microprocessors, etc.

In a firmware or software configuration, the exemplary embodiment of thepresent invention may be achieved by a module, a procedure, a function,etc. performing the above-described functions or operations. Forexample, software code may be stored in the memory units 2080 and 2090and executed by the processors 2020 and 2030. The memory units arelocated at the interior or exterior of the processor and may transmitdata to and receive data from the processor via various known means.

The embodiments of the present invention may be carried out in otherspecific ways without departing from the spirit and essentialcharacteristics of the present invention. The above detailed descriptionis therefore to be construed in all aspects as illustrative and notrestrictive. The scope of the invention should be determined by theappended claims and their legal equivalents, not by the abovedescription, and all changes coming within the meaning and equivalencyrange of the appended claims are intended to be embraced therein. Also,claims that are not explicitly cited in the appended claims may bepresented in combination as an exemplary embodiment of the presentinvention or included as a new claim by subsequent amendment after theapplication is filed.

The embodiments of the present invention may be applied to variouswireless access systems, for example, a 3GPP LTE system, a 3GPP LTE-Asystem, a 3GPP2 system, and/or an IEEE, 802.16m system. The embodimentsof the present invention may be applied to all technical fields applyingthe various wireless access systems, as well as the various wirelessaccess systems.

What is claimed is:
 1. A method for reporting Channel State Information(CSI) in a wireless access system which supports carrier aggregation,the method performed by a user equipment (UE) and comprising: measuringa first type CSI for a first component carrier (CC) of two or moredownlink (DL) CCs; measuring a second type CSI for a second CC of thetwo or more downlink (DL) CCs; and reporting the first type CSI only,when a collision of a report of the first type CSI with a report of thesecond CSI type occurs in a same subframe, wherein the first type CSIincludes (1) a Rank Indicator (RI) and a first Precoding MatrixIndicator (PMI), (2) only the RI, or (3) only the first PMI, and whereinthe second type CSI includes (1) a Wideband Channel Quality Indicator(WB-CQI) and a second PMI, (2) the WB-CQI and the first PMI, or (3) onlythe WB-CQI.
 2. The method according to claim 1, wherein the first typeCSI has higher priority an the second type CSI and the second type CSIis dropped.
 3. The method according to claim 1, further comprising:receiving information related to a CSI reporting mode for each of thetwo or more DL CCs, wherein the measurements of the first type CSI andthe second type CSI are performed based on the CSI reporting mode. 4.The method according to claim 1, wherein the reporting the first typeCSI is periodically performed according to each content of the firsttype CSI.
 5. The method according to claim 1, wherein the first type CSIis reported through a Physical Uplink Control Channel (PUCCH) or aPhysical Uplink Shared Channel (PUSCH).
 6. A user equipment (UE) forreporting Channel State Information (CSI) in a wireless access systemwhich supports carrier aggregation, the UE comprising: a transmitter; areceiver; and a processor configured to control the transmitter and thereceiver for reporting the CSI, wherein the processor is furtherconfigured to: measure a first type CSI for a first component carrier(CC) of two or more downlink (DL) CCs; measure a second type CSI for asecond CC of the two or more downlink (DL) CCs; and report the firsttype CSI only thought the transmitter, when a collision of a report ofthe first type CSI with a report of the second CSI type occurs in a samesubframe, wherein the first type CSI includes (1) a Rank Indicator (RI)and a first Precoding Matrix Indicator (PMI), (2) only the RI, or (3)only the first PMI, and wherein the second type CSI includes (1) aWideband Channel Quality Indicator (WB-CQI) and a second PMI, (2) theWB-CQI and the first PMI, or (3) only the WB-CQI.
 7. The UE according toclaim 6, wherein the first type CSI has higher priority than the secondtype CSI and the second type CSI is dropped.
 8. The UE according toclaim 6, where the processor is further configured to: receiveinformation related to a CSI reporting mode for each of the two or moreDL CCs through the receiver, wherein the measurements of the first typeCSI and the second type CSI are performed based on the CSI reportingmode.
 9. The UE according to claim 6, wherein the reporting the firsttype CSI is periodically performed according to each content of thefirst type CSI.
 10. The UE according to claim 6, wherein the first typeCST is reported through a Physical Uplink Control Channel (PUCCH) or aPhysical Uplink Shared Channel (PUSCH).